As a wireless communication system in which a wireless access point and a wireless terminal communicate with each other, the wireless local area network (LAN) that adopts carrier sense multiple access/collision avoidance (CSMA/CA) is widely known. In the wireless LAN technology, the downlink multiuser MIMO (DL-MU-MIMO) technique, an extension of the Multi-Input Multi-Output (MIMO) technique, is known. In the downlink multiuser MIMO, a technology called beamforming is used, which allows an access point to perform data transmission to wireless terminals with beams spatially orthogonal to one another. Therefore, different pieces of data can be transmitted to a plurality of wireless terminals simultaneously. Each wireless terminal having been received the piece of data notifies, to the access point, whether the piece of data has been received without error (acknowledgement response), and issues a retransmission request for data that has not been successfully received.
The wireless terminals having received data transmit acknowledgement response frames to the access point in turns while shifting a time. Therefore, an overhead occurs by the number of terminals, which hinders the achievement of a high throughput.